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Aerospace, Volume 9, Issue 5 (May 2022) – 54 articles

Cover Story (view full-size image): The availability of different types of data and advances in data-driven techniques open the path to more-detailed analyses of various phenomena. Using data mining techniques, we analyze historical flight trajectories, aiming to identify the usual choices that airlines make in terms of routing and how they relate to aircraft types and operational flight costs. The clustering is applied to intra-European trajectories during a summer season, and a statistical test of independence is used to evaluate the relationships between the variables of interest. The findings show that statistically significant relationships between the trajectory clusters and the operating airlines (in about 49% of city pairs), the aircraft types (30%), and/or the flight costs (45%) are found for flights longer than 1000 km. View this paper
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Article
Assessment of Future Airframe and Propulsion Technologies on Sustainability of Next-Generation Mid-Range Aircraft
Aerospace 2022, 9(5), 279; https://doi.org/10.3390/aerospace9050279 - 23 May 2022
Viewed by 548
Abstract
The present work demonstrates the impact of future airframe and propulsion technologies on the sustainability of potential future medium-range commercial jets with design specifications similar to the Airbus A320-200. Advanced airframe and engine technologies include laminar flow control (LFC), active load alleviation, new [...] Read more.
The present work demonstrates the impact of future airframe and propulsion technologies on the sustainability of potential future medium-range commercial jets with design specifications similar to the Airbus A320-200. Advanced airframe and engine technologies include laminar flow control (LFC), active load alleviation, new materials and structures, and ultra-high bypass ratio turbofan engines. Two aircraft configurations with various design options were compared to determine potentially the best option for the mission profile, which tends to minimize the environmental impact. Each configuration was designed to balance the equivalent CO2 emissions and Direct Operating Costs. Technology sensitivity analyses were performed to investigate the significance of particular technology combinations and determine the ones that improve aircraft sustainability the most. All studies were performed at a conceptual design level using a multi-fidelity design approach to investigate the system-level effects of the technologies. The open-source aircraft design environment SUAVE was extended and integrated with other aircraft design and analysis tools to obtain all required correlations. The aircraft with advanced technologies showed an average reduction in equivalent CO2 emissions of 36% and a 23% reduction in DOC compared to the reference aircraft for a similar mission profile, although aircraft with future technologies may have a 43% higher production cost. The given results indicate that the application of technologies may be commercially successful if technologies achieve expected performance values, despite high development costs. Finally, the technology sensitivity analysis demonstrated the most significant influence of engine-related technologies and laminar flow control compared to other technologies considered in this research. Depending on design and integration complexities, engine technologies can be more achievable in the near future and can substantially reduce the overall emission level. Full article
(This article belongs to the Special Issue Aircraft Design (SI-4/2022))
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Article
Model and Optimization of the Tether for a Segmented Space Elevator
Aerospace 2022, 9(5), 278; https://doi.org/10.3390/aerospace9050278 - 22 May 2022
Viewed by 535
Abstract
In order to improve the shortcomings of the traditional constant section and gradual section space elevator system, combined with the advantages of constant section and gradual section space elevator system, a model of segmented space elevator system is designed. This model has the [...] Read more.
In order to improve the shortcomings of the traditional constant section and gradual section space elevator system, combined with the advantages of constant section and gradual section space elevator system, a model of segmented space elevator system is designed. This model has the characteristics of easier construction, more practical functions, and easier maintenance. The cyclic iterative method is proposed to calculate the stress distribution of the space elevator system. The maximum stress variation and system scale variation of segmented space elevator system with different segment numbers is analyzed and compared with the system scale of constant section and gradual section space elevator system. The results show that the segmented space elevator model can significantly reduce the peak stress of the space elevator system under the condition of limited increase in the system scale, and the peak stress is 56% lower than that of the constant section space elevator model. Considering the number of segments, peak stress, and system scale, the calculation results show that the optimal number of segments is 5 or 6. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Nonlinear Covariance Analysis-Based Robust Rendezvous Trajectory Design by Improved Differential Evolution Method
Aerospace 2022, 9(5), 277; https://doi.org/10.3390/aerospace9050277 - 21 May 2022
Viewed by 504
Abstract
This paper presents a robust trajectory design method for approaching and rendezvous with a space target considering multi-source uncertainties. A nonlinear covariance analysis method based on the state transition tensor is presented to formulate the propagation of uncertainties including environment parameter uncertainty, actuator [...] Read more.
This paper presents a robust trajectory design method for approaching and rendezvous with a space target considering multi-source uncertainties. A nonlinear covariance analysis method based on the state transition tensor is presented to formulate the propagation of uncertainties including environment parameter uncertainty, actuator error, sensor noise, navigation error and initial state dispersion of the closed-loop GN&C system. Then, the robust trajectory design problem is defined based on the quantified effect of the uncertainties, and an improved self-adaptive differential evolution algorithm is presented to solve the robust trajectory design problem with uncertainties. Finally, four groups of numerical simulations are carried out to show that the designed robust trajectories can satisfy the final state dispersion constraint under multi-source uncertainties. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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Article
Real-Time Fuel Optimization and Guidance for Spacecraft Rendezvous and Docking
Aerospace 2022, 9(5), 276; https://doi.org/10.3390/aerospace9050276 - 20 May 2022
Viewed by 571
Abstract
Autonomous rendezvous and docking (RVD) fuel optimization with field-of-view and obstacle avoidance constraints is a nonlinear and nonconvex optimization problem, making it computationally intensive for onboard computation on CubeSats. This paper proposes an RVD fuel optimization and guidance technique suitable for onboard computation [...] Read more.
Autonomous rendezvous and docking (RVD) fuel optimization with field-of-view and obstacle avoidance constraints is a nonlinear and nonconvex optimization problem, making it computationally intensive for onboard computation on CubeSats. This paper proposes an RVD fuel optimization and guidance technique suitable for onboard computation on CubeSats, considering the shape, size and computational limitations of CubeSats. The computation time is reduced by dividing the guidance problem into separate orbit and attitude guidance problems, formulating the orbit guidance problem as a convex optimization problem by considering the CubeSat shape, and then solving the orbit guidance problem with a convex optimization solver and the attitude guidance problem analytically by exploiting the attitude geometry. The performance of the proposed guidance method is demonstrated through simulations, and the results are compared with those of conventional methods that perform orbit guidance optimization with attitude quaternion feedback control. The proposed method shows better performance, in terms of fuel efficiency, than conventional methods. Full article
(This article belongs to the Topic Micro/Nano Satellite Technology, Systems and Components)
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Article
Conceptual Design of a Hybrid Hydrogen Fuel Cell/Battery Blended-Wing-Body Unmanned Aerial Vehicle—An Overview
Aerospace 2022, 9(5), 275; https://doi.org/10.3390/aerospace9050275 - 19 May 2022
Viewed by 714
Abstract
The manuscript presents the conceptual design phase of an unmanned aerial vehicle, with the objective of a systems approach towards the integration of a hydrogen fuel-cell system and Li-ion batteries into an aerodynamically efficient platform representative of future aircraft configurations. Using a classical [...] Read more.
The manuscript presents the conceptual design phase of an unmanned aerial vehicle, with the objective of a systems approach towards the integration of a hydrogen fuel-cell system and Li-ion batteries into an aerodynamically efficient platform representative of future aircraft configurations. Using a classical approach to aircraft design and a combination of low- and high-resolution computational simulations, a final blended wing body UAV was designed with a maximum take-off weight of 25 kg and 4 m wingspan. Preliminary aerodynamic and propulsion sizing demonstrated that the aircraft is capable of completing a 2 h long mission powered by a 650 W fuel cell, hybridized with a 100 Wh battery pack, and with a fuel quantity of 80 g of compressed hydrogen. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology II)
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Article
Track Segment Association Method Based on Bidirectional Track Prediction and Fuzzy Analysis
Aerospace 2022, 9(5), 274; https://doi.org/10.3390/aerospace9050274 - 19 May 2022
Viewed by 509
Abstract
Due to sensor characteristics, geographical environment, electromagnetic interference, electromagnetic silence, information countermeasures, and other reasons, the phenomenon of track breakages occur in the process of aircraft track data processing. It leads to the change in target label attributes. In order to make the [...] Read more.
Due to sensor characteristics, geographical environment, electromagnetic interference, electromagnetic silence, information countermeasures, and other reasons, the phenomenon of track breakages occur in the process of aircraft track data processing. It leads to the change in target label attributes. In order to make the track segment association effect better, we studied several existing time series prediction methods, and proposed a track segment association method based on bidirectional Holt-Winters prediction and fuzzy analysis. This algorithm bidirectionally predicts and extrapolates track segments by the Holt-Winters method, and then uses the fuzzy track segment association algorithm to perform segment association and secondary association. The simulation results of this method show that the track segment association method based on Holt-Winters prediction and fuzzy analysis can effectively solve the track association problem where the target label attributes change before and after track breakage, demonstrating better association ability and robustness. Compared with the fuzzy association method without adding track prediction, our method generally improves the association accuracy by 35%. Full article
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Article
Performance Evaluation of Multiflight Ground Handling Process
Aerospace 2022, 9(5), 273; https://doi.org/10.3390/aerospace9050273 - 18 May 2022
Viewed by 529
Abstract
The ever-increasing high density of flights arouses an urgent requirement to improve the effectiveness and performance of ground handling in airport operation. The implementation of coordinated airport decision-making quantifies the ground handling process into a series of key milestone nodes, which is more [...] Read more.
The ever-increasing high density of flights arouses an urgent requirement to improve the effectiveness and performance of ground handling in airport operation. The implementation of coordinated airport decision-making quantifies the ground handling process into a series of key milestone nodes, which is more conducive for operators to reduce resource consumption and flight delays. An innovative performance evaluation method for the multiflight ground handling process is proposed based on shared information of milestone nodes in the ground handling. A dynamic performance evaluation model is established, which should superimpose the performance evaluation results of the single-flight ground handling process. Meanwhile, the indicators and weights of the single-flight performance evaluation are obtained by combining the ground handling process prediction and expected value. As time evolves, a matrix method for the multiflight ground handling performance evaluation is proposed to combine the logic and evolution of the process. It is shown that the average prediction accuracy of single-flight ground handling process nodes can be increased to 87.63%. The experimental analysis demonstrates that the objectivity, effectiveness and dynamics of the proposed approach can be the basis for short-term tactics in airport. Full article
(This article belongs to the Section Air Traffic and Transportation)
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Article
Coordinated Formation Guidance Law for Fixed-Wing UAVs Based on Missile Parallel Approach Method
Aerospace 2022, 9(5), 272; https://doi.org/10.3390/aerospace9050272 - 18 May 2022
Viewed by 533
Abstract
This paper presents a classic missile-type parallel-approach guidance law for fixed-wing UAVs in coordinated formation flight. The key idea of the proposed guidance law is to drive each follower to follow the virtual target point. Considering the turning ability of each follower, the [...] Read more.
This paper presents a classic missile-type parallel-approach guidance law for fixed-wing UAVs in coordinated formation flight. The key idea of the proposed guidance law is to drive each follower to follow the virtual target point. Considering the turning ability of each follower, the formation form adopts the semi-perfect rigid form, which does not require the vehicle positions form a rigid formation, and the orientations keep consensus. According to the mission characteristics of the follower following a leader and the leader following a route, three guidance laws for straight, turning, and circling flight are designed. A series of experiments demonstrate the proposed guidance law’s improved response and maneuvering stability. The results of hardware-in-the-loop simulations and real flight tests prove that the proposed guidance law satisfies the practical UAV formation flight control demands. Full article
(This article belongs to the Section Aeronautics)
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Article
Aerodynamic Uncertainty Quantification for Tiltrotor Aircraft
Aerospace 2022, 9(5), 271; https://doi.org/10.3390/aerospace9050271 - 18 May 2022
Viewed by 550
Abstract
The tiltrotor has unique flight dynamics due to the aerodynamic interference characteristics. Multiple aerodynamics calculation approaches, such as the CFD method, are utilised to characterise this feature. The calculation process is usually time-consuming, and the obtained results are generally varied from each other. [...] Read more.
The tiltrotor has unique flight dynamics due to the aerodynamic interference characteristics. Multiple aerodynamics calculation approaches, such as the CFD method, are utilised to characterise this feature. The calculation process is usually time-consuming, and the obtained results are generally varied from each other. Thus, the uncertainty quantification (UQ) method will be utilised in this research to identify the aerodynamic inaccuracy effect on the handling qualities of the tiltrotor aircraft. The study aims to quantify the influence of the aerodynamic interference on the tiltrotor flight dynamics in different flight states, such as forward speeds and nacelle tilting angles, which can guide the flight dynamics modelling simplification to improve the simulation efficiency. Therefore, uncertainty identification and full factorial numerical integration (FFNI) methods are introduced to scale these aerodynamic uncertainties. The eigenvalue and bandwidth and phase delay requirements are presented as the failure criteria. The UQ calculation indicates that the uncertainties of the aerodynamic calculation significantly affect the handling quality ratings in two flight ranges: the helicopter mode and the conversion and aeroplane modes with higher forward speed (close to the conversion envelope). Furthermore, a sensitivity analysis is performed to identify the mechanism behind these influences. The results demonstrate that aerodynamics affect the pitching attitude, the pitching damping, and the velocity and incidence stability derivatives. However, the effects of the velocity stability and the incidence stability are the reason causing the handling qualities’ degradation in the helicopter mode and high-speed mode, respectively. Full article
(This article belongs to the Section Aeronautics)
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Article
A Cyber-Physical Prototyping and Testing Framework to Enable the Rapid Development of UAVs
Aerospace 2022, 9(5), 270; https://doi.org/10.3390/aerospace9050270 - 17 May 2022
Viewed by 540
Abstract
In this work, a cyber-physical prototyping and testing framework to enable the rapid development of UAVs is conceived and demonstrated. The UAV Development Framework is an extension of the typical iterative engineering design and development process, specifically applied to the rapid development of [...] Read more.
In this work, a cyber-physical prototyping and testing framework to enable the rapid development of UAVs is conceived and demonstrated. The UAV Development Framework is an extension of the typical iterative engineering design and development process, specifically applied to the rapid development of UAVs. Unlike other development frameworks in the literature, the presented framework allows for iteration throughout the entire development process from design to construction, using a mixture of simulated and real-life testing as well as cross-aircraft development. The framework presented includes low- and high-order methods and tools that can be applied to a broad range of fixed-wing UAVs and can either be combined and executed simultaneously or be executed sequentially. As part of this work, seven novel and enhanced methods and tools were developed that apply to fixed-wing UAVs in the areas of: flight testing, measurement, modeling and emulation, and optimization. A demonstration of the framework to quickly develop an unmanned aircraft for agricultural field surveillance is presented. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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Article
A Clustering Ensemble Method of Aircraft Trajectory Based on the Similarity Matrix
Aerospace 2022, 9(5), 269; https://doi.org/10.3390/aerospace9050269 - 17 May 2022
Viewed by 526
Abstract
Performing clustering analysis on a large amount of historical trajectory data can obtain information such as frequent flight patterns of aircraft and air traffic flow distribution, which can provide a reference for the revision of standard flight procedures and the optimization of the [...] Read more.
Performing clustering analysis on a large amount of historical trajectory data can obtain information such as frequent flight patterns of aircraft and air traffic flow distribution, which can provide a reference for the revision of standard flight procedures and the optimization of the division of airspace sectors. At present, most trajectory clustering uses a single clustering algorithm. When other processing remains unchanged, it is difficult to improve the clustering effect by using a single clustering method. Therefore, this paper proposes a trajectory clustering ensemble method based on a similarity matrix. Firstly, a stacked autoencoder is used to learn a small number of features that are sufficiently representative of the trajectory and used as the input to the subsequent clustering algorithm. Secondly, each basis cluster is used to cluster the data set, and then a consistent similarity matrix is obtained by using the clustering results of each basis cluster. On this basis, using the deformation of the matrix as the distance matrix between trajectories, the agglomerative hierarchical clustering algorithm is used to ensemble the results of each basis cluster. Taking the Nanjing Lukou Airport terminal area as an example, the experimental results show that integrating multiple basis clusters eliminates the inherent randomness of a single clustering algorithm, and the trajectory clustering results are more robust. Full article
(This article belongs to the Section Air Traffic and Transportation)
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Article
Thermal Design of Blackbody for On-Board Calibration of Spaceborne Infrared Imaging Sensor
Aerospace 2022, 9(5), 268; https://doi.org/10.3390/aerospace9050268 - 16 May 2022
Viewed by 499
Abstract
In this study, we propose a thermal design for an on-board blackbody (BB) for spaceborne infrared (IR) sensor calibration. The main function of the on-board BB is to provide highly uniform and precise radiation temperature reference sources from 0 °C to 40 °C [...] Read more.
In this study, we propose a thermal design for an on-board blackbody (BB) for spaceborne infrared (IR) sensor calibration. The main function of the on-board BB is to provide highly uniform and precise radiation temperature reference sources from 0 °C to 40 °C during the calibration of the IR sensor. To meet the functional requirements of BB, a BB thermal design using a heater to heat the BB during sensor calibration and heat pipes to transfer residual heat to the radiator after calibration is proposed and investigated both numerically and experimentally. The main features of the proposed thermal design are a symmetric temperature gradient on the BB surface with less than 1 K temperature uniformity, ease of temperature sensor implementation to estimate the representative surface temperature of the BB, a stable thermal interface between the heat pipes and BB, and a fail-safe function under one heat pipe failure. The thermal control performance of the BB is investigated via in-orbit thermal analysis, and its effectiveness is verified via a heat-up test of the BB under ambient conditions. These results indicate that the temperature gradient on the BB surface was obtained at less than 1 K, and the representative surface temperature could be estimated with an accuracy of 0.005 °C via the temperature sensor. Full article
(This article belongs to the Special Issue Advanced Small Satellite Technology)
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Article
Experimental Investigation of a Cylindrical Air-Breathing Continuous Rotating Detonation Engine with Different Nozzle Throat Diameters
Aerospace 2022, 9(5), 267; https://doi.org/10.3390/aerospace9050267 - 16 May 2022
Viewed by 527
Abstract
A continuous detonation engine with various exhaust nozzles, analogous to typical scramjet cavity combustors with variable rear-wall heights, was adopted to perform a succession of cylindrical air-breathing continuous rotating detonation experiments fueled by a non-premixed ethylene/air mixture. The results show that the detonation [...] Read more.
A continuous detonation engine with various exhaust nozzles, analogous to typical scramjet cavity combustors with variable rear-wall heights, was adopted to perform a succession of cylindrical air-breathing continuous rotating detonation experiments fueled by a non-premixed ethylene/air mixture. The results show that the detonation combustion was observed to self-sustain in the combustor through simultaneous high-speed imaging covering the combustor and isolator. A long test, lasting more than three seconds, was performed in this unique configuration, indicating that the cylindrical isolator–combustor engine exhibits potential for practical applications. Three distinct combustion modes were revealed with varied equivalent ratios (hybrid mode, sawtooth wave mode, and deflagration mode). The diameter of the nozzle throat was critical in the formation of rotating detonation waves. When the nozzle throat diameter was larger than the specific value, the detonation wave could not form and self-sustain. The upstream boundary of the shock train was supposed to be close to the isolator entrance in conditions of a high equivalence ratio and small nozzle throat diameter. In addition, it was verified that periodic high-frequency pressure oscillation could cause substantial impacts on the incoming flow as compared with the steady deflagration with the same combustor pressure. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Long-Term Orbit Prediction and Deorbit Disposal Investigation of MEO Navigation Satellites
Aerospace 2022, 9(5), 266; https://doi.org/10.3390/aerospace9050266 - 15 May 2022
Viewed by 611
Abstract
With the increase in satellites in the medium Earth orbit (MEO) region, there should be a focus on orbit safety in the MEO region. A safe orbit disposal strategy is necessary to maintain the sustainability of the MEO region. This paper focuses on [...] Read more.
With the increase in satellites in the medium Earth orbit (MEO) region, there should be a focus on orbit safety in the MEO region. A safe orbit disposal strategy is necessary to maintain the sustainability of the MEO region. This paper focuses on long-term evolution modeling, safety analysis of MEO objects, and different disposal techniques for end-of-life BDS-2 MEO satellites. On the one hand, a long-term numerical evolution model is established, and mean equinoctial elements are adopted to propagate a long-term orbit. Long-term evolution for the MEO region over 100 years is carried out, including the Galileo, BDS, GPS, and GLONASS constellations. The earliest orbit intersection time with other global navigation satellite system (GNSS) constellations is put forward. On the other hand, a dynamic model and an optimization model for disposal orbit are established, which minimize the eccentricity growth within 200 years and the fuel consumption for maneuvering to the disposal orbit. The bounds for the disposal region of BDS MEO satellites are also proposed, which consider the measurement and control error of BDS MEO satellites and the eccentricity bounds for end-of-life BDS MEO satellites. A genetic algorithm is adopted to optimize the orbital elements for end-of-life BDS MEO satellites. In addition, two disposal cases, namely, upraising and reducing the orbit, for end-of-life BDS MEO satellites are simulated. The long-term evolutions for the disposal of orbital elements within 200 years are implemented, and the fuel consumption is calculated. The results show that the current MEO region is relatively safe and that the eccentricity is the most important factor that influences the long-term evolution of safety analysis for BDS MEO disposal orbits. Upraising the orbit is safe for end-of-life BDS MEO satellites. This investigation provides the theoretical foundation for investigating the long-term evolutionary mechanisms of the MEO region and references disposal strategy analysis for decommissioned navigation satellites, and the spent upper stages for other GNSS constellations. Full article
(This article belongs to the Topic GNSS Measurement Technique in Aerial Navigation)
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Article
A Modal Interpretation for Aeroelastic Stability Enhancement of Mistuned Bladed Disks
Aerospace 2022, 9(5), 265; https://doi.org/10.3390/aerospace9050265 - 13 May 2022
Viewed by 554
Abstract
Understanding the mechanism of the aeroelastic stability improvement induced by mistuning is essential for the design of bladed disks in aero-engines. In this paper, a quantitative interpretation is given. It starts by projecting the mistuned aeroelastic modes into the space spanned by the [...] Read more.
Understanding the mechanism of the aeroelastic stability improvement induced by mistuning is essential for the design of bladed disks in aero-engines. In this paper, a quantitative interpretation is given. It starts by projecting the mistuned aeroelastic modes into the space spanned by the tuned modes. In this way, the mistuned aeroelastic damping can be expressed by the superposition of the tuned damping. Closed-form expressions are found, providing clear interpretations of several frequently reported trends in the literature. Further, a prediction approach is proposed, where the analysis of aeroelastic coupling only needs to be performed once, and it is decoupled from the analysis of the mistuning effect. The advantages are two-fold. First, the design of the mistuning pattern is accelerated. Second, this allows one to introduce more accurate data or models of aeroelastic damping. An empirical bladed disk with NASA-ROTOR37 profile is used as an example, and the alternate, wave, and random patterns are considered. Full article
(This article belongs to the Section Aeronautics)
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Article
Design, Analysis, and Testing of a Scaled Propeller for an Innovative Regional Turboprop Aircraft
Aerospace 2022, 9(5), 264; https://doi.org/10.3390/aerospace9050264 - 13 May 2022
Viewed by 640
Abstract
This paper describes the design, numerical analyses, and wind tunnel tests of the scaled model of a propeller serving as a propulsive element for the experimental tests of an advanced regional turboprop aircraft with engines installed on the horizontal tailplane tips. The design [...] Read more.
This paper describes the design, numerical analyses, and wind tunnel tests of the scaled model of a propeller serving as a propulsive element for the experimental tests of an advanced regional turboprop aircraft with engines installed on the horizontal tailplane tips. The design has been performed by complying with the thrust similarity from the full-scale aircraft propulsive requirements. Numerical analyses with a high-fidelity aerodynamic solver confirmed that the initial design made with XROTOR would achieve the expected performance. Finally, a strengthened version of the propeller has been manufactured via 3D printing and tested in the wind tunnel. Test data include measurements of thrust as well as propeller normal force at different angles of attack. Good agreement between numerical and experimental results has been observed, enabling the propeller to be used confidently in the aircraft wind tunnel powered test campaign. Full article
(This article belongs to the Special Issue Turboprop Aircraft Design and Optimization)
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Article
Aircraft-Type-Specific Impact of Speed Brakes on Lift and Drag
Aerospace 2022, 9(5), 263; https://doi.org/10.3390/aerospace9050263 - 12 May 2022
Viewed by 610
Abstract
The increasing influence of current research in air traffic management on daily flight operations leads to a stronger consideration of individually optimized aircraft trajectories. However, in the dichotomy between ecological, economic, and safety-based optimization goals, four-dimensionally optimized trajectories are subject to severe constraints [...] Read more.
The increasing influence of current research in air traffic management on daily flight operations leads to a stronger consideration of individually optimized aircraft trajectories. However, in the dichotomy between ecological, economic, and safety-based optimization goals, four-dimensionally optimized trajectories are subject to severe constraints in terms of position and speed. To fully assess the performance envelope of these trajectories, precise modelling of the influence of secondary control surfaces on flight performance is necessary. In particular, the use of speed brakes can significantly influence the descent and speed profile and allows the implementation of different cost indices. In this study, we present a modelling approach of the influence of extended speed brakes on flight performance and apply this method in a simulation environment for trajectory modelling of twelve different aircraft types. In doing so, we can determine an almost linear influence of the additional fuel requirement from the effective area of the speed brakes. The results can be implemented in any flight performance model and enable more precise modelling of future aircraft trajectories. Specifically, optimization targets regarding the required time of arrival, or the cost index and the consideration of the dynamic impact of atmospheric conditions in the trajectory optimization, only becomes possible through the calculation of the influence of the speed brake on lift and drag. Full article
(This article belongs to the Special Issue Re-Searching Flight Performance)
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Article
Aerodynamic Interference on Trim Characteristics of Quad-Tiltrotor Aircraft
Aerospace 2022, 9(5), 262; https://doi.org/10.3390/aerospace9050262 - 12 May 2022
Viewed by 558
Abstract
The aerodynamic interference between the different components of quad-tiltrotor (QTR) aircraft were considered to analyze its influence on trim characteristics. A comprehensive method with the fixed-wake model was developed for multiple aerodynamic interactions, improving the accuracy of the flight dynamics analysis. Additionally, a [...] Read more.
The aerodynamic interference between the different components of quad-tiltrotor (QTR) aircraft were considered to analyze its influence on trim characteristics. A comprehensive method with the fixed-wake model was developed for multiple aerodynamic interactions, improving the accuracy of the flight dynamics analysis. Additionally, a more general control strategy was developed to tackle the redundant control issue of the QTR, improving its control efficiency by coordinating the authority relationship of various control surfaces across the flight range. Then, the trim features were calculated in the helicopter mode, conversion mode, and airplane mode, and the relevant results with and without interaction were compared. The results show that the aerodynamic interaction mainly influences the body’s vertical force, longitudinal force, and pitching moment. Furthermore, there are significant differences between collective and longitudinal sticks and pitch attitudes. The interference plays a major role in helicopter and conversion modes with a less-than-30-degree tilt angle. Full article
(This article belongs to the Section Aeronautics)
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Article
Numerical Simulation of Tiltrotor Flow Field during Shipboard Take-Off and Landing Based on CFD-CSD Coupling
Aerospace 2022, 9(5), 261; https://doi.org/10.3390/aerospace9050261 - 12 May 2022
Viewed by 592
Abstract
Due to the small tilt angle, a tiltrotor operates in non-axial flow conditions during shipboard take-off and landing. The non-uniformity of the blade’s air-load is high, resulting in structural deformation with high fluctuation frequency, affecting the rotor’s aerodynamic characteristics. A new computational fluid-dynamic [...] Read more.
Due to the small tilt angle, a tiltrotor operates in non-axial flow conditions during shipboard take-off and landing. The non-uniformity of the blade’s air-load is high, resulting in structural deformation with high fluctuation frequency, affecting the rotor’s aerodynamic characteristics. A new computational fluid-dynamic computational structural dynamics (CFD-CSD) solver is proposed to analyze the effects of the blade’s elastic deformation on the aerodynamic characteristics. This method is suitable for the aeroelastic simulation of shipboard tiltrotor take-offs and landings. The CFD method uses the Reynolds-averaged Navier-Stokes (RANS) equations as the control equation, while the CSD solver is based on the Timoshenko beam model. The solvers are combined with a two-way loose coupling strategy to improve the solution efficiency. The reverse overset assembly technique (ROAT) is utilized to eliminate the effects of orphan mesh points after deformation. The simulation is conducted during take-off and landing at different heights and different tilt angles, using the XV-15 tiltrotor as an example. An analysis of the rotor’s air-load and the mutual interference of the vortex and wake indicates that when the tiltrotor takes off or lands with a small tilt angle, the wing shedding vortex causes the rotor’s wake to roll upward before it reaches the ship’s deck, producing strong thrust fluctuations. The elastic deformation of the blade reduces the fluctuations in the thrust amplitude. This phenomenon is more pronounced in areas of high fluctuations in the blade’s air-load. Full article
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Article
Dynamic Response of Structurally Reinforced Wing Leading Edge against Soft Impact
Aerospace 2022, 9(5), 260; https://doi.org/10.3390/aerospace9050260 - 11 May 2022
Viewed by 594
Abstract
In this current research, a commercial aircraft metallic leading edge structurally reinforced with a Y-shaped and V-shaped plate system is numerically examined to investigate the effectiveness of such reinforcements against soft impacts, more commonly known as bird strikes in the aviation industry. A [...] Read more.
In this current research, a commercial aircraft metallic leading edge structurally reinforced with a Y-shaped and V-shaped plate system is numerically examined to investigate the effectiveness of such reinforcements against soft impacts, more commonly known as bird strikes in the aviation industry. A non-linear finite element code Ansys Explicit is adopted to run the virtual test cases. The computational bird model is presented with the Lagrange algorithm and Mooney–Rivlin hyperelastic material parameters which are validated against the experimental data found in the literature. A second validation of the leading edge deformation pattern is also carried out to ensure the accuracy of the present work. Numerical outcomes suggest that due to the presence of the reinforcement, the leading edge skin is restrained from being drastically deformed and the bird model tears apart into two pieces requiring the leading edge model to absorb much less kinetic energy. Additionally, it is found that both the reinforcements have similar crashworthiness performance against bird impacts. The novelty of the research lies in founding the structural reinforcement as a primary preference to strengthen the vulnerable wing leading edge during bird impacts. Full article
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Article
Angular Displacement Control for Timoshenko Beam by Optimized Traveling Wave Method
Aerospace 2022, 9(5), 259; https://doi.org/10.3390/aerospace9050259 - 11 May 2022
Viewed by 559
Abstract
The vibration of flexible structures in spacecraft, such as large space deployable reflectors, solar panels and large antenna structure, has a great impact on the normal operation of spacecraft. Accurate vibration control is necessary, and the control of angular displacement is a difficulty [...] Read more.
The vibration of flexible structures in spacecraft, such as large space deployable reflectors, solar panels and large antenna structure, has a great impact on the normal operation of spacecraft. Accurate vibration control is necessary, and the control of angular displacement is a difficulty of accurate control. In the traditional control method, the mode space control has a good effect on suppressing low-order modes, but there is control overflow. The effect of traveling wave control on low-order modes is worse than the former, but it has the characteristics of broadband control. It can better control high-order modes and reduce control overflow. In view of the advantages and disadvantages of the two control methods, based on Timoshenko beam theory, this paper uses vector mode function to analyze the modal of spacecraft cantilever beam structure, establishes the system dynamic equation, and puts forward an optimized traveling wave control method. As a numerical example, three strategies of independent mode space control, traditional traveling wave control and optimized traveling wave control are used to control the active vibration of beam angle. By comparing the numerical results of the three methods, it can be seen that the optimal control method proposed in this paper not only effectively suppresses the vibration, but also improves the robustness of the system, reflecting good control performance. An innovation of this paper is that the Timoshenko beam model is adopted, which considers the influence of transverse shear deformation and moment of inertia on displacement and improves the accuracy of calculation, which is important for spacecraft accessory structures with high requirements for angle control. Another innovation is that the optimized traveling wave control method is exquisite in mathematical processing and has good results in global and local vibration control, which is not available in other methods. Full article
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Article
Geostationary Orbital Debris Collision Hazard after a Collision
Aerospace 2022, 9(5), 258; https://doi.org/10.3390/aerospace9050258 - 10 May 2022
Viewed by 618
Abstract
Many space objects are densely distributed in the geostationary (GEO) band, and the long-term impact of the collision of GEO spacecraft and space debris on the GEO environment has attracted more and more attention. After summarizing the advantages and disadvantages of the long-term [...] Read more.
Many space objects are densely distributed in the geostationary (GEO) band, and the long-term impact of the collision of GEO spacecraft and space debris on the GEO environment has attracted more and more attention. After summarizing the advantages and disadvantages of the long-term evolution model based on the “Cube” collision probability calculation model, the “Grid” model, a long-term evolution model especially suitable for GEO band, was established. For four types of collision and disintegration events, the “Grid” model was used to study the space environment in the GEO band after collisions between GEO spacecraft and space debris. Future collisions were simulated, and the number of space objects in the next 100 years was counted. Once space debris and massive spacecraft were completely disintegrated after collision, the number of space objects and the collision probability increased sharply, and this caused a collision cascading syndrome. Even if there was no initial disintegration event, collision and disintegration events occurred in the long-term evolution of the GEO band, which led to an increase in the number of space objects. However, the collision probability was much lower, and the number of space objects grew much more slowly without the initial collision. Full article
(This article belongs to the Special Issue Space Debris Removal: Challenges and Opportunities)
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Article
Maneuvering Spacecraft Orbit Determination Using Polynomial Representation
Aerospace 2022, 9(5), 257; https://doi.org/10.3390/aerospace9050257 - 10 May 2022
Viewed by 605
Abstract
This paper proposed a polynomial representation-based method for orbit determination (OD) of spacecraft with the unknown maneuver. Different from the conventional maneuvering OD approaches that rely on specific orbit dynamic equation, the proposed method needs no priori information of the unknown maneuvering model. [...] Read more.
This paper proposed a polynomial representation-based method for orbit determination (OD) of spacecraft with the unknown maneuver. Different from the conventional maneuvering OD approaches that rely on specific orbit dynamic equation, the proposed method needs no priori information of the unknown maneuvering model. The polynomials are used to represent the unknown maneuver. A transformation is made for the polynomials to improve the convergence and robustness. The Extended Kalman Filter (EKF) is used to process incoming observation data by compensating the unknown maneuver using the polynomials. The proposed method is successfully applicated into the OD problem of spacecraft with trigonometric maneuver. Numerical simulations show that the eighth-order polynomials are accurate enough to represent a trigonometric maneuver. Moreover, Monte Carlo simulations show that the position errors are smaller than 1 km, and the maneuver estimated errors are no more than 0.1 mm/s2 using the eighth-order polynomials. The proposed method is accurate and efficient, and has potential applications for tracking maneuvering space target. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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Article
Influence of Fluid Viscosity and Compressibility on Nonlinearities in Generalized Aerodynamic Forces for T-Tail Flutter
Aerospace 2022, 9(5), 256; https://doi.org/10.3390/aerospace9050256 - 09 May 2022
Viewed by 653
Abstract
The numerical assessment of T-tail flutter requires a nonlinear description of the structural deformations when the unsteady aerodynamic forces comprise terms from lifting surface roll motion. For linear flutter, a linear deformation description of the vertical tail plane (VTP) out-of-plane bending results in [...] Read more.
The numerical assessment of T-tail flutter requires a nonlinear description of the structural deformations when the unsteady aerodynamic forces comprise terms from lifting surface roll motion. For linear flutter, a linear deformation description of the vertical tail plane (VTP) out-of-plane bending results in a spurious stiffening proportional to the steady lift forces, which is corrected by incorporating second-order deformation terms in the equations of motion. While the effect of these nonlinear deformation components on the stiffness of the VTP out-of-plane bending mode shape is known from the literature, their impact on the aerodynamic coupling terms involved in T-tail flutter has not been studied so far, especially regarding amplitude-dependent characteristics. This term affects numerical results targeting common flutter analysis, as well as the study of amplitude-dependent dynamic aeroelastic stability phenomena, e.g., Limit Cycle Oscillations (LCOs). As LCOs might occur below the linear flutter boundary, fundamental knowledge about the structural and aerodynamic nonlinearities occurring in the dynamical system is essential. This paper gives an insight into the aerodynamic nonlinearities for representative structural deformations usually encountered in T-tail flutter mechanisms using a CFD approach in the time domain. It further outlines the impact of geometrically nonlinear deformations on the aerodynamic nonlinearities. For this, the horizontal tail plane (HTP) is considered in isolated form to exclude aerodynamic interference effects from the studies and subjected to rigid body roll and yaw motion as an approximation to the structural mode shapes. The complexity of the aerodynamics is increased successively from subsonic inviscid flow to transonic viscous flow. At a subsonic Mach number, a distinct aerodynamic nonlinearity in stiffness and damping in the aerodynamic coupling term HTP roll on yaw is shown. Geometric nonlinearities result in an almost entire cancellation of the stiffness nonlinearity and an increase in damping nonlinearity. The viscous forces result in a stiffness offset with respect to the inviscid results, but do not alter the observed nonlinearities, as well as the impact of geometric nonlinearities. At a transonic Mach number, the aerodynamic stiffness nonlinearity is amplified further and the damping nonlinearity is reduced considerably. Here, the geometrically nonlinear motion description reduces the aerodynamic stiffness nonlinearity as well, but does not cancel it. Full article
(This article belongs to the Special Issue Aeroelasticity, Volume III)
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Article
Additive Manufacturing of Novel Hybrid Monolithic Ceramic Substrates
Aerospace 2022, 9(5), 255; https://doi.org/10.3390/aerospace9050255 - 07 May 2022
Viewed by 623
Abstract
Additive manufacturing (AM) can revolutionise engineering by taking advantage of unconstrained design and overcoming the limitations of traditional manufacturing capabilities. A promising application of AM is in catalyst substrate manufacturing, aimed at the enhancement of the catalytic efficiency and reduction in the volume [...] Read more.
Additive manufacturing (AM) can revolutionise engineering by taking advantage of unconstrained design and overcoming the limitations of traditional manufacturing capabilities. A promising application of AM is in catalyst substrate manufacturing, aimed at the enhancement of the catalytic efficiency and reduction in the volume and weight of the catalytic reactors in the exhaust gas aftertreatment systems. This work addresses the design and fabrication of innovative, hybrid monolithic ceramic substrates using AM technology based on Digital Light Processing (DLP). The designs are based on two individual substrates integrated into a single, dual-substrate monolith by various interlocking systems. These novel dual-substrate monoliths lay the foundation for the potential reduction in the complexity and expense of the aftertreatment system. Several examples of interlocking systems for dual substrates were designed, manufactured and thermally post-processed to illustrate the viability and versatility of the DLP manufacturing process. Based on the findings, the sintered parts displayed anisotropic sintering shrinkage of approximately 14% in the X–Y direction and 19% in the Z direction, with a sintered density of 97.88 ± 0.01%. Finally, mechanical tests revealed the mechanical integrity of the designed interlocks. U-lock and Thread configurations were found to sustain more load until complete failure. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ceramic Materials in Aerospace)
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Article
SpaceDrones 2.0—Hardware-in-the-Loop Simulation and Validation for Orbital and Deep Space Computer Vision and Machine Learning Tasking Using Free-Flying Drone Platforms
Aerospace 2022, 9(5), 254; https://doi.org/10.3390/aerospace9050254 - 06 May 2022
Viewed by 696
Abstract
The proliferation of reusable space vehicles has fundamentally changed how assets are injected into the low earth orbit and beyond, increasing both the reliability and frequency of launches. Consequently, it has led to the rapid development and adoption of new technologies in the [...] Read more.
The proliferation of reusable space vehicles has fundamentally changed how assets are injected into the low earth orbit and beyond, increasing both the reliability and frequency of launches. Consequently, it has led to the rapid development and adoption of new technologies in the aerospace sector, including computer vision (CV), machine learning (ML)/artificial intelligence (AI), and distributed networking. All these technologies are necessary to enable truly autonomous “Human-out-of-the-loop” mission tasking for spaceborne applications as spacecrafts travel further into the solar system and our missions become more ambitious. This paper proposes a novel approach for space-based computer vision sensing and machine learning simulation and validation using synthetically trained models to generate the large amounts of space-based imagery needed to train computer vision models. We also introduce a method of image data augmentation known as domain randomization to enhance machine learning performance in the dynamic domain of spaceborne computer vision to tackle unique space-based challenges such as orientation and lighting variations. These synthetically trained computer vision models then apply that capability for hardware-in-the-loop testing and evaluation via free-flying robotic platforms, thus enabling sensor-based orbital vehicle control, onboard decision making, and mobile manipulation similar to air-bearing table methods. Given the current energy constraints of space vehicles using solar-based power plants, cameras provide an energy-efficient means of situational awareness when compared to active sensing instruments. When coupled with computationally efficient machine learning algorithms and methods, it can enable space systems proficient in classifying, tracking, capturing, and ultimately manipulating objects for orbital/planetary assembly and maintenance (tasks commonly referred to as In-Space Assembly and On-Orbit Servicing). Given the inherent dangers of manned spaceflight/extravehicular activities (EVAs) currently employed to perform spacecraft maintenance and the current limitation of long-duration human spaceflight outside the low earth orbit, space robotics armed with generalized sensing and control and machine learning architecture have a unique automation potential. However, the tools and methodologies required for hardware-in-the-loop simulation, testing, and validation at a large scale and at an affordable price point are in developmental stages. By leveraging a drone’s free-flight maneuvering capability, theater projection technology, synthetically generated orbital and celestial environments, and machine learning, this work strives to build a robust hardware-in-the-loop testing suite. While the focus of the specific computer vision models in this paper is narrowed down to solving visual sensing problems in orbit, this work can very well be extended to solve any problem set that requires a robust onboard computer vision, robotic manipulation, and free-flight capabilities. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Spaceborne Atom-Interferometry Gravity Gradiometry Design towards Future Satellite Gradiometric Missions
Aerospace 2022, 9(5), 253; https://doi.org/10.3390/aerospace9050253 - 06 May 2022
Viewed by 597
Abstract
Atom-interferometry gravity gradiometry has been developed as a promising technique for future gravity gradiometric missions after GOCE due to its greater sensitivity in micro-gravity environments and constant performance over the measurement bandwidth. In this paper, a feasible method of spaceborne atom-interferometry gravity gradiometry [...] Read more.
Atom-interferometry gravity gradiometry has been developed as a promising technique for future gravity gradiometric missions after GOCE due to its greater sensitivity in micro-gravity environments and constant performance over the measurement bandwidth. In this paper, a feasible method of spaceborne atom-interferometry gravity gradiometry is proposed by utilizing the free-fall condition of the cold atoms in space. Compared with GOCE, which shows an in-orbit noise performance of 10~20 mE/Hz1/2, the scheme described in this paper would achieve a high sensitivity of 1.9 mE/Hz1/2 for gravity gradients measurement by reducing the orbital altitude and optimizing the interrogation time for atom interferometry. The results show that the proposed scheme could significantly augment the spectral content of the gravity field in the degree and order of 280~316 and resolve the global gravity field with an improved accuracy of 0.2 [email protected] km and 0.85 [email protected] km in terms of geoid height, and 0.06 [email protected] km and 0.3 [email protected] km in terms of gravity anomaly after 1270 days of data collection. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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Article
Modelling and Stabilisation of an Unconventional Airship: A Polytopic Approach
Aerospace 2022, 9(5), 252; https://doi.org/10.3390/aerospace9050252 - 05 May 2022
Viewed by 595
Abstract
The paper presents the modelling and stabilisation of an unconventional airship. The complexity of such a new design requires both proper dynamic modelling and control. A complete dynamic model is built here. Based on the developed dynamic model, a nonlinear control law is [...] Read more.
The paper presents the modelling and stabilisation of an unconventional airship. The complexity of such a new design requires both proper dynamic modelling and control. A complete dynamic model is built here. Based on the developed dynamic model, a nonlinear control law is proposed for this airship to evaluate its sensitivity during manoeuvres above a loading area. The proposed stabilisation controller derives its source from a polytopic quasi-Linear Parameter varying (qLPV) model of the nonlinear system. A controller, which takes into account certain modelling uncertainties and the stability of the system, is analysed using Lyapunov’s theory. Finally, to facilitate the design of the controller, we express the stability conditions using Linear Matrix Inequalities (LMIs). Numerical simulations are presented to highlight the power of the proposed controller. Full article
(This article belongs to the Special Issue Mission Analysis and Design of Lighter-than-Air Flying Vehicles)
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Article
A Civil Aircraft Cockpit Layout Evaluation Method Based on Layout Design Principles
Aerospace 2022, 9(5), 251; https://doi.org/10.3390/aerospace9050251 - 04 May 2022
Viewed by 604
Abstract
As technology continues to leap forward and innovations advance, the systems of civil aircraft are becoming increasingly sophisticated and complex. Accordingly, there is a rising amount of information to be processed by pilots in the cockpit, increasing their cognitive burden, which significantly threatens [...] Read more.
As technology continues to leap forward and innovations advance, the systems of civil aircraft are becoming increasingly sophisticated and complex. Accordingly, there is a rising amount of information to be processed by pilots in the cockpit, increasing their cognitive burden, which significantly threatens the safety of flight. Thus, designers have formulated cockpit layout principles relating to importance, frequency of use, functional grouping, and operation sequence on the basis of ergonomics, which can effectively reduce the cognitive burden for pilots. The degree to which the cockpit layout of a model conforms to the four design principles can indicate its ergonomic design level. In accordance with the concepts of the above four cockpit layout principles, evaluation methods for determining their respective conformity to the four design principles were proposed in this paper. These methods use the operational sequence of cockpit system controls used in the normal flight mission of the actual aircraft type as the evaluation data source. Subsequently, the total evaluation results for cockpit layout were obtained using the weighted accumulation method. Lastly, the process for evaluating the cockpit layouts of civil aircraft was illustrated using the cockpits of the A320 series and B737NG series as examples. Based on the final evaluation results, the feasibility and effectiveness of the proposed evaluation method was verified. Full article
(This article belongs to the Section Aeronautics)
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Article
A Counterfactual Framework Based on the Machine Learning Method and Its Application to Measure the Impact of COVID-19 Local Outbreaks on the Chinese Aviation Market
Aerospace 2022, 9(5), 250; https://doi.org/10.3390/aerospace9050250 - 04 May 2022
Viewed by 623
Abstract
COVID-19 affects aviation around the world. China’s civil aviation almost recovered to its pre-epidemic levels in the domestic market, but there are still local outbreaks that affect air traffic. This paper proposes measuring the impact of local outbreaks of COVID-19 by the machine [...] Read more.
COVID-19 affects aviation around the world. China’s civil aviation almost recovered to its pre-epidemic levels in the domestic market, but there are still local outbreaks that affect air traffic. This paper proposes measuring the impact of local outbreaks of COVID-19 by the machine learning method and the synthetic control method as a counterfactual control group to measure such an impact. In this study, we use the LightGBM algorithm to construct a counterfactual control group and transform the prediction problem from time series to the fitting problem at the spatial level. We find that machine learning methods can measure such an impact more accurately. We take local outbreaks in Beijing and Dalian as examples, and our measure of their impacts shows that the impact of an outbreak on intercity air traffic can be divided into lag, decline, stable, and recovery periods, and will last for a long period (more than 40 days) unless there are external stimuli, such as legal holidays. The outbreaks reduced the number of passengers in the cities by 90%. Finally, we show the impact on the air traffic network, and find that when a local outbreak happens in a big city, tourist cities or small stations will be greatly affected. Full article
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